The present invention generally relates to a motion estimating apparatus to be used in the efficient coding of motion picture signals based on differences between frames.
A so-called block matching algorithm has been employed as one technique for motion estimation. In this technique, each successive picture is divided into small blocks. The motion associated with any particular block is detected by calculating a predicted error between the block in a present picture and each of respective blocks located within a certain interval from the same position of the block in a succeeding picture. The predicted errors of the blocks in the succeeding picture with respect to the block of the present picture are compared. A position of a block in the succeeding picture in which the predicted error is the smallest is deemed to be a motion compensated position with respect to the block of the present picture. The positional difference between the block of the present picture and the motion compensated position is designated a motion vector of the block. A full search method or a tree search method, such as a 3-step method or the like, is employed to obtain the predicted errors. The 3-step searching method is used as a method of reducing the calculating time as compared with the full search method.
The conventional embodiments of a block matching algorithm and a 3-step searching method are described in the publication entitled "Discrete Cosine Transform Algorithms, Advantages, Applications" by K. R. Rao and P. Yip 1990 ACADEMIC PRESS, INC.
In the conventional method, a summation is carried out of the predicted errors of all the pixels within the block, whereby a problem arises in that the number of calculations and hardware scale become larger as the search range is expanded and/or as the size of the motion estimation block becomes larger, thus making it difficult to increase the detection accuracy.